Published European Patent Documents EP-C-0 306 766 and EP-C-0 230 804 disclose metallic cylinder head gaskets for internal combustion engines. These prior art gaskets comprise carrier plate which cooperates with at least one cover plate, the cover plate having resilient beads, i.e., deformations, which function as sealing rings. The gap at any point between the cylinder head and cylinder block of an internal combustion engine varies during operation as a function of the working cycle of the adjacent cylinder. The cylinder head gasket, which must seal this variable gap, is subjected to constant changes in pressure and must have permanent resilient properties in order to maintain a satisfactory seal.
The seal established by the gaskets of the above-identified references is created by upward extensions of the cylinder head gasket, such extensions being disposed about the combustion spaces, and the beads. The beads act as spring elements and follow vertical relative movements of the cylinder head in relation to the cylinder block which occur as a result of cylinder pressure variations. On the one hand, no unacceptably large deformation of a sealing bead must occur when the bead is subjected to maximum load. On the other hand, the relief of the applied, i.e., clamping, force must not be complete but rather only take place to such an extent that a minimum deformation occurs. The working range of the bead lies between these two limit points of the deformation.
In order to ensure proper functioning thereof, the beads must not be completely deformed either during the installation of the gasket or in the operating state. An unacceptably large deformation of a bead vertically with respect to the plane of the gasket is prevented in known gaskets by means of a deformation limiter of constant thickness. The deformation limiters also serve to extend the gasket upwardly along the combustion space.
Translatory movements can occur between the cylinder block and the cylinder head when these engine components have coefficients of thermal expansion, a cast iron block combined with a light weight, i.e., aluminum, metal head, for example. Translatory movements can also occur if the cooling conditions are different. Translatory movements lead to erosion created leakage paths, particularly on the cylinder head.
Published German Patent Document DE-A-4 219 709 discloses deformation limiters of rectangular cross-section produced by extrusion or heading. In the case of extrusion produced limiters, since the material being worked flows in all directions and not only in the desired direction, there are large material stresses with a so-called "frog effect" corresponding to a frog spring. For products formed by heading, a conical die is required. Use of such a die leads to uneven edges and the method is unsuitable for mass production since the product is not formed with precise repeatability.
Therefore, an object of the invention is to provide a metallic cylinder head gasket, and a method of fabrication thereof, in which the maximum acceptable deformation of the bead is not exceeded even over relatively long operation.
Another object of the invention is to provide a metallic cylinder head gasket designed to eliminate the formation of leakage channels in the cylinder head.